Known are electric switches (multiplexers, demultiplexers, data switches) by which two or more data streams are combined or separated or by which combined data streams are switched.
In conventional, electric transmission systems, digital data is commonly transmitted using time-division multiplexing, i.e., by interleaving data of different connections in time.
Here, both time-division-multiplex channels, i.e., associated time slots with a fixed spacing, and calls using cells inserted into a data stream at irregular intervals must be mentioned. The former is the STM technique (STM=Synchronous Transfer Mode), which has long been known but has only recently been termed so, and the latter is the ATM technique (ATM=Asynchronous Transfer Mode).
In conventional, electric transmission systems, the combination, particularly the switching, of such time-division multiplex data streams is effected using space-division and time-division multiplexing.
For optical signal transmission, comparable switches are to be provided. For space-division switching, i.e., the switching of an optical signal from one optical signal path to another, there are already sufficient practicable solutions. Time-division switching, which involves buffering, has been solved in principle, but for practical applications, particularly for the switching of optical ATM signals, the solutions are unsuitable.